Such a device is disclosed in EP 1 396 234 B1, for example. The device there, designed as a pen needle and used to hold a needle, has webs which are distributed about the circumference of its hollow cylindrical main body and which extend from the proximal end in the direction of the distal end of the main body, and the webs open out into an elevation which is designed as a bead and which is formed at the distal end about the entire circumference of the main body. Depressions are formed about the circumference of the main body by the webs. These depressions begin at the proximal end of the main body and extend in the direction of the distal end thereof, but without reaching the distal end. The webs and depressions thus formed serve to release a used pen needle from an injection pen and at the same time to dispose of it in a suitable disposal container. When the pen needle is to be disposed of, it is fitted into an opening of the disposal container, which opening corresponds approximately to the dimension of the pen needle. Elements corresponding to the webs and depressions of the pen needle are arranged on this opening, about a part of the circumference, and form a negative image of the webs and depressions of the pen needle.
To release the pen needle, the injection pen is therefore inserted, with the pen needle toward the front, into the opening of the disposal container until the webs and depressions of the pen needle engage in the corresponding elements of the opening. In this position, the pen needle, which has been screwed with an inner thread onto an outer thread of the injection pen, is unscrewed from the injection pen and engaged from behind by an abutment. Thereafter, the injection pen is moved away from the opening of the disposal container. Ideally, the pen needle with its webs and depressions should then release itself from the corresponding elements of the opening and drop into the disposal container, in which it is then safely stored.
However, it has been shown that, with the pen needle thus released from the injection pen, the elevation extending about its entire circumference at the open end and designed in particular as a bead catches on or becomes wedged in the elements of the disposal container that correspond to the webs and depressions of the pen needle. The pen needle therefore sticks in the opening of the disposal container and is not yet safely disposed of therein. To complete the safe disposal in the container, it is necessary in such a case for the stuck or wedged pen needle to be pushed by hand or with a tool into the disposal container. In doing so, there is a risk that the person wishing to dispose of the pen needle may be injured by the needle protruding from the opening of the disposal container. Such a needlestick injury is of course also associated with a not inconsiderable risk of life-threatening infection under some circumstances, since such devices for injection of liquids may be used by persons with highly infectious diseases.
In other pen needles according to the prior art, the pen needle is likewise engaged from behind by an abutment on the disposal container during release, in which case a gap is created between pen needle and injection pen, such that the known pen needles can be released from the injection pen by means of engagement from behind. To this extent, all of the known pen needles are dependent on the geometry of the injection pen from which they are released.